In-vitro study of fracture strength and marginal adaptation of fibre-reinforced adhesive fixed partial inlay dentures

Fracture load and failure mode of semi-direct resin composite occlusal veneers: Influence of design and mechanical cycling

AIMS

To evaluate the influence of the type of preparation and mechanical cycling on the fracture load and failure mode of semi-direct posterior resin composite restorations.

METHODS

In total, 70 healthy third molars were used; 10 belonging to the control group (C - unprepared teeth) and 60 teeth prepared and restored with nanoparticle resin composite, divided into 3 groups (n = 20): O - exclusively occlusal preparation (Table Top); OV - occlusal preparation with buccal extension (Veneerlay); OVP - Occlusal preparation with chamfer on the proximal and buccal-lingual/palatal surfaces (Overlay). The preparations were performed with diamond burs with a thickness of 1 mm. The restorations were made with nanoparticulate resin composite (Filtek Z350 XT) and subsequently received additional polymerization (thermoprocessing). Cementation was performed with the use of universal adhesive system (Single Bond Universal) on dental substrate and dual resin cement (RelyX ARC). Half of the teeth in each group (n = 10) were submitted to mechanical cycling, simulating 6 months of clinical service (5 × 105 fatigue cycles), under dynamic loading of 130 N, at a frequency of 2Hz. Fracture load tests were performed in a universal testing machine with a 200 kgf load cell. Failure mode was classified using scores. Generalized linear models and Fisher Exact tests were applied to the data (significance level of 5%).

RESULTS

There were no significant differences between the types of preparation (p = 0.9435), or relative to cycling (p = 0.3764). The Fisher Exact Test showed a significant association between the groups and the type of failure (p = 0.0006), with preparations O (with cycling) and OVP (with and without cycling) exhibiting most failures with restoration fractures without involvement of the dental remnant.

CONCLUSIONS

Semi-direct restorations showed resistance to fracture load similar to that of healthy teeth and were capable of withstanding functional masticatory loads. The type of preparation influenced the failure mode of teeth. The Table Top and Overlay types of preparations were those had fewer catastrophic failures, suggesting that since they are more conservative preparations, they made it possible for the tooth to receive a new restorative procedure in the future in cases of failures.

Validation of a shape-optimized 2-unit cantilevered inlay-retained fiber-reinforced resin-bonded dental prosthesis

STATEMENT OF PROBLEM

Current designs of fiber-reinforced composite (FRC) resin-bonded fixed dental prostheses (RBFDPs) have a limited lifespan, failing mainly through veneer-fiber delamination, debonding, and fracture.

PURPOSE

The purpose of this in vitro study was to validate a new inlay-retained 2-unit cantilevered RBFDP with an optimized cavity and fiber layout proposed in a previous study by using simulated occlusal loading.

MATERIAL AND METHODS

Two groups of specimens (n=20), 1 with and 1 without glass fibers, were used to test the influence of the cavity design and that of the fiber layout on their load capacity, respectively. The specimens without fibers were directly cut from a resin-ceramic block by using a computer-aided manufacturing system, while those with fibers were manually fabricated with unidirectional glass fibers and composite resin in a silicone mold. The specimens with and without fibers were attached to abutments made of the same resin-ceramic with a cyanoacrylate-based adhesive and a resin-based dental cement, respectively. An increasing compressive load was applied on the mesial fossa of the premolar pontic until failure. Cracking in the specimens during loading was monitored with a 2-channel acoustic emission (AE) system.

RESULTS

All the specimens without fiber reinforcement debonded from the abutments. Those using the optimized shovel-shaped cavity design had a mean ±standard deviation failure load (50.0 ±17.3 N) that was 193% higher than that of those with the conventional step-box design (17.1 ±6.2 N; P<.001). No significant difference was found between the groups for the mean number of AE events per specimen (step-box: 49 ±34 versus shovel-shaped: 63 ±34; P=.427), the mean amplitude of each event (58.4 ±1.3 dB versus 59.5 ±2.4 dB; P=.299), or the mean time to failure (283.2 ±122.3 seconds versus 297.5 ±66.7 seconds; P=.798). Between the groups of specimens with reinforcing fibers, the mean failure load of the conventional design was approximately half that of the optimized one. Again, no significant difference was found for the mean number of AE events per specimen (conventional: 28 ±18 versus optimized: 52 ±53; P=.248) or the mean amplitude for each AE event (64.9 ±4.2 dB versus 61.7 ±5.2 dB; P=.187). The connectors of 8 fiber-reinforced specimens with the conventional design fractured; the other 2 debonded from the abutments. Half of the shape-optimized fiber-reinforced specimens had fractured abutments, but the cantilevers remained intact, 4 specimens fractured at the connector, and only 1 debonded from its abutment.

CONCLUSIONS

The shape-optimized 2-unit cantilevered FRC RBFDP had a higher load capacity than the conventional design.

In-vitro performance of posterior fiber reinforced composite (FRC) bridge with different framework designs

This study aimed to investigate the effect of various framework designs on the failure of posterior fiber reinforced composite (FRC) bridges and assess the post crack performances of the repaired prostheses. Thirty samples were prepared into three different groups of framework designs: cuspal support (CS), anatomic features (AF) and circular reinforcement (CR). All specimens were subjected to static loading test and acoustic emission analysis. Significant differences were found in the load and time of initial failures among the three groups (p<0.001). CS was identified as the optimum framework design. Samples with composite delamination at the pontic site were selected and repaired with a clinically simplified protocol. Significant differences were also observed between the repaired and original FRC bridges (p=0.01). The performance of these prostheses was highly dependent on the framework design and the perspective of repairing FRC bridges may warrant future investigations.

Load bearing capacity and Weibull characteristics of inlay-retained resin-bonded fixed dental prosthesis made of all-ceramic, fiber-reinforced composite and metal-ceramic after cyclic loading

PURPOSE

The objectives of this study were to evaluate the load bearing capacity of RBFDPs made of different materials after cyclic loading, and classify the failure types after loading.

MATERIALS AND METHODS

Sound human mandibular first premolars and first molar pairs (N = 60 per tooth type, n = 10 per group) were randomly divided into six experimental groups to receive one of the following inlay-retained RBFDP types: RC: Resin composite only, DFRC: Direct E-glass fiber-reinforced composite (FRC), IFRC: Indirect E-glass FRC, LS: Lithium disilicate glass-ceramic, ZR: Yttria-stabilized tetragonal zirconia, MC: Metal-ceramic. Box preparations were made in abutment teeth using diamond burs followed by standardized ultrasonic burs. The teeth were conditioned employing an etch-and-rinse adhesive system and the indirect RBFDPs were cemented adhesively. The specimens were subjected to cyclic loading for x1.200.000 in distilled water alternating between 5 and 55 °C (Zurich Chewing Simulator). They were then loaded to failure from the occlusal surface in the Universal Testing Machine (cross-head speed: 1 mm/min). Failure types were classified as repairable or irreparable depending on the location and size. Data were analyzed using Welch and Tamhane's T2 post-hoc tests (α = 0.05). Weibull modulus for each group was calculated based on parametric distribution analysis of censored data for maximum fracture load.

RESULTS

Mean load bearing capacity (N) of Groups LS (1274 ± 270), ZR (1567 ± 363) and MC (1544 ± 787) were significantly higher than those of other groups (p < 0.05). RC, DFRC, IFRC (601 ± 130 - 819 ± 270) and MC did not show significant difference (p > 0.05). Weibull modulus (m) was the highest in Group LS (m = 5.3) followed by Group RC (m = 5.1). Other groups presented Weibull moduli ranging between 1.4 and 3.3. Only in Group ZR, 2 early debonding occurred during cyclic loading. While in this group predominantly irreparable failures (debonding with without tooth fracture) were observed (8 out of 10), all other groups presented mainly single or a combination of repairable failures (chipping in the veneering material). DFRC, IDRC and MC did not show any debonding from the abutment teeth.

CONCLUSION

Considering load bearing capacity, repairable failure types and Weibull moduli, lithium disilicate seem to be more durable than those of other material options for posterior inlay-retained RBFDPs. Due to early debondings and catastrophic irreparable failure types, zirconia RBFDPs should be indicated with caution in the posterior region.

Effect of fiber-reinforcement on the strength of polymer materials for provisional restorations: An in vitro study

OBJECTIVE

The purpose of this study was to evaluate the effect of three different methods of fiber reinforcement (glass fibers preimpregnated, glass fibers nonpreimpregnated, and polyethylene fibers) on the flexural strength and modulus of elasticity of poly-methyl-methacrylate resin (PMMA) and Bis-Gma materials.

MATERIALS AND METHODS

A total of 60 specimens of autopolymerizing PMMA resin specimens were fabricated using a stainless steel matrix with dimensions of (37.5± 2) × (3 ± 0.1) × (3 ± 0.1) mm according to the standards of ISO 10477. The autopolymerizing resins used in this study were: (a) JET, (b) TRIM, (c) PROTEMP. The fibers used in this study were STICK (Glass fiber preimpregnated), POLYDENTIA (Glass fiber nonpreimpregnated), RIBBOND (Polyethylene fiber). The specimens were tested by three-point bending test and the flexural strength and modulus of elasticity were recorded. The data of each resin type were analyzed by analysis of variance using a significance level of 0.05 to determine the mean differences.

RESULTS

The integration of reinforcing fibers in the mass of resins for provisional restorations increased both the flexural strength and the modulus of elasticity in all tested combinations compared to control groups. After the three-point bending test, the specimens were not completely fractured and the parts remained together due to the fibers.

CONCLUSIONS

Fiber reinforcement is an effective method to increase mechanical properties of provisional restorative resins. Reinforcement with fibers enhances the flexural strength and the modulus of elasticity of the specimens compared to unreinforced (control) group.

CLINICAL SIGNIFICANCE

The reinforcement of resin materials used for provisional restorations with fibers can increase mechanical strength and may improve the clinical performance and the longevity of provisional restorations during their clinical function.

Fracture Resistance of CAD/CAM Lithium Disilicate of Endodontically Treated Mandibular Damaged Molars Based on Different Preparation Designs

The aim of this study was to evaluate the fracture resistance of 2 different types of all-ceramic crown using immediate dentin sealing (IDS), obtained using a CAD/CAM system on molars with different preparations. Forty extracted lower molars were endodontically treated and divided into four groups (n = 10) according to the dental preparation. Group 1 (SP0) was prepared without filling the pulp chamber and crown-root junction was located at the cementoenamel junction (CEJ). Group 2 (SP1) was prepared without filling the pulp chamber and crown-root junction was located 1-mm above the CEJ. Groups 3 and 4 contained a flat preparation surface with no axial wall height. Group 3 (CP0) was made IDS with complete filling of the pulp chamber with composite resin and crown-root junction was located at the CEJ. Group 4 (CP1) was prepared with complete filling of the pulp chamber and crown-root junction was located 1-mm above the CEJ. All groups were restored with CAD/CAM lithium disilicate ceramic crowns. Specimens were subjected to the fracture test and statistically analyzed using analysis of variance (ANOVA). Fracture mode was determined using a stereoscopic microscope, classified as repairable or nonrepairable, and analyzed using Fischer's exact test. Results indicated that there were no significant differences between the groups in terms of fracture resistance or fracture pattern (p >0.05). Fracture resistance was the lowest in the SP0 group, followed by the SP1 group (1634.38 N) of CP0 (1821.50 N), and it was the highest in the CP1 group. There was a predominance of nonrepairable fractures and there were no significant differences in the fracture resistance and fracture mode of CAD/CAM lithium disilicate molar all-ceramic crowns. Endodontically treated molars teeth might be restored with endocrowns or all-ceramic crowns on flat preparation; however tooth fracture failures that affect reliability of these types of restorations should be considered.

Reproducibility of different coping arrangements fabricated by dental micro-stereolithography: Evaluation of marginal and internal gaps in metal copings

Background/purpose

To evaluate the reproducibility of the marginal and internal gaps of metal copings fabricated using dental micro-stereolithography (μ-SLA), which is an additive manufacturing system.

Materials and methods

A study cast of abutment tooth 46 was made from type-IV dental stone and was scanned to create a standard triangulation language file. Arrays of one (ORM), three (TRM), and six (SRM) resin copings were then fabricated on the μ-SLA build platform using investment, burnout, and casting (n = 12). The marginal and internal gaps of these metal copings were measured using a silicone-replica technique with a digital microscope (×160). The data obtained were analyzed using a non-parametric Kruskal–Wallis H test, a post-hoc Mann–Whitney U test, and a Bonferroni correction.

Results

The mean and standard deviation of the marginal gap for each group were measured and found to be 81.1 and 53.2 μm, 68.3 and 44.8 μm, and 90.3 and 57.7 μm for ORM, TRM, and SRM, respectively. There were no statistical differences in the marginal gaps of the three groups (p > 0.05).

Conclusion

The marginal and internal gap of ORM, TRM and SRM groups were considered clinically acceptable.

Fracture resistance and stress distribution of repairing endodontically treated maxillary first premolars with severe non-carious cervical lesions

This study was to compare the influence of glass fiber post placement and crown restoration on endodontically treated maxillary first premolars with severe NCCLs using three-dimensional finite element analysis and fracture resistance testing. G1, intact teeth. G2, teeth with artificial defect. G3, composite resin (CR). G4, CR and fiber post in buccal canal (FPB). G5, CR and fiber post in palatal canal (FPP). G6, CR and fiber posts in buccal and palatal canals (FPBP). G7, CR and crown (C). G8, CR, FPB, C. G9, CR, FPP, C. G10, CR, FPBP, C. Teeth in G2, G3, and G5 showed a similar stress concentration at the tip of the defect. The fracture resistance of G2 did not differ significantly from G3 and G5 (p>0.05) but differed significantly from that in other groups (p<0.05). The fractures in G4 were more favorable, and the difference of those in G1 from those in G7, G8, G9, and G10 was statistically significant (p<0.05). Restoration of root-filled maxillary premolars with severe NCCLs using fiber post in the buccal canal may be more efficacious than other restoration methods.

Displacement of teeth without and with bonded fixed orthodontic retainers: 3D analysis using triangular target frames and optoelectronic motion tracking device

PURPOSE

The objective of this study was to evaluate the anterior tooth movement without and with bonded fixed orthodontic retainers under incremental loading conditions.

MATERIALS AND METHODS

Six extracted mandibular anterior human teeth were embedded in acrylic resin in True Form I Arch type and 3D reconstruction of Digital Volume Tomography (DVT) images (0.4 mm³ voxels) were obtained. The anatomy of each tooth was segmented and digitally reconstructed using 3D visualization software for medical images (AMIRA, FEI SVG). The digital models of the teeth were repositioned to form an arch with constant curvature using a CAD software (Rhinoceros) and a base holder was designed fitting the shape of the roots. The clearance between the roots and their slot in the holder was kept constant at 0.3 mm to replicate the periodontal ligament thickness. The holder and the teeth were then manufactured by 3D printing (Objet Eden 260VS, Stratasys) using a resin material for dental applications (E = 2-3 GPa). The 3D-printed teeth models were then positioned in the holder and the root compartments were filled with silicone. The procedure was repeated to obtain three identical arch models. Each model was tested for tooth mobility by applying force increasing from 5 to 30 N with 5 N increments applied perpendicular on the lingual tooth surface on the incisal one third (crosshead speed: 0.1 mm/s). The teeth on each model were first tested without retainer (control) and subsequently with the bonded retainers (braided bonded retainer wire; Multi-strand 1 × 3 high performance wire, 0.022″ × 0.016″). Tooth displacement was measured in terms of complicance (F/Δ movement) (N/mm) using custom-built optoelectronic motion tracking device (OPTIS) (accuracy: 5 µm; sampling rate: 200 Hz). The position of the object was detected through three LEDs positioned in a fixed triangular shape on a metal support (Triangular Target Frame). The measurements were repeated for three times for each tooth. Data were analyzed using mixed model with nesting (alpha = 0.05).

RESULTS

The use of retainer showed a significant effect on tooth mobility (0.008 ± 0.004) compared to non-bonded teeth (control) (0.014 ± 0.009) (p < 0.0001). The amount of displacement on the tooth basis was also significantly different (p = 0.0381) being the most for tooth no. 42 (without: 0.024 ± 0.01; with: 0.012 ± 0.002) (p = 0.0018). No significant difference was observed between repeated measurements (p = 0.097) and the incremental magnitude of loading (5-30 N: 0.07 ± 0.01-0.09 ± 0.02) (p > 0.05).

CONCLUSION

Mandibular anterior teeth showed less tooth mobility when bonded with stainless steel wire as opposed to non-bonded teeth but the tooth mobility varied depending on the tooth type. Intermittent increase in loading from 5 to 30 N did not increase tooth displacement.

The influence of polymerization type and reinforcement method on flexural strength of acrylic resin

The aim of this study was to evaluate the flexural strength of acrylic resin bars by varying the types of resin polymerization and reinforcement methods. Fourteen groups (N = 10) were created by the interaction of factors in study: type of resin (self-cured (SC) or heat-cured (HC)) and reinforcement method (industrialized glass fiber (Ind), unidirectional glass fiber (Uni), short glass fiber (Short), unidirectional and short glass fiber (Uni-Short), thermoplastic resin fiber (Tpl), and steel wire (SW)). Reinforced bars (25 × 2 × 2 mm) were tested in flexural strength (0.5 mm/min) and examined by scanning electron microscopy (SEM). Data (MPa) were submitted to factorial analysis, ANOVA, and Tukey and T-student tests (a = 5%) showing significant interaction (P = 0.008), for SC: Uni (241.71 ± 67.77)^a, Uni-Short (221.05 ± 71.97)^a, Ind (215.21 ± 46.59)^ab, SW (190.51 ± 31.49)^abc, Short (156.31 ± 28.76)^bcd, Tpl (132.51 ± 20.21)^cd, Control SC (101.47 ± 19.79)^d and for HC: Ind (268.93 ± 105.65)^a, Uni (215.14 ± 67.60)^ab, Short (198.44 ± 95.27)^abc, Uni-Short (189.56 ± 92.27)^abc, Tpl (161.32 ± 62.51)^cd, SW (106.69 ± 28.70)^cd, and Control HC (93.39 ± 39.61)^d. SEM analysis showed better fiber-resin interaction for HC. Nonimpregnated fibers, irrespective of their length, tend to improve fracture strength of acrylics.

Effect of different design preparations on the flexural and fracture strength of fiber-reinforced composite fixed partial dentures: an in vitro study

PURPOSE

To determine and compare the flexural and fracture strength of three-unit fiber-reinforced composite (FRC) fixed partial dentures (FPDs) using three abutment design preparations.

MATERIAL AND METHODS

The flexural and fracture strength of three-unit FRC FPDs were evaluated using three design preparations of the abutments (conventional full crown [group A], box-shaped [group B], and tub-shaped [group C]). Thirty three-unit FRC FPDs were fabricated (10 specimens per group) for the replacement of missing mandibular first molars and were adhesively luted to extracted human teeth. The flexural and fracture strength were determined using a universal testing machine with a steel loading pin of 20 mm diameter with a 3-mm-diameter hardened circular tip. Each specimen was evaluated under SEM to determine mode of failure.

RESULTS

Mean fracture strength for group A was 820.00 ± 56.51 N, group B was 536.94 ± 65.62 N, and group C was 501.24 ± 66.71 N. The highest mean flexural strength was found in group A (68.33 ± 4.71 MPa), followed by group B (44.74 ± 5.46 MPa) and lowest in group C (41.77 ± 5.56 MPa). The SEM evaluation showed partial or complete debonding of veneering composite from fiber framework, leaving intact fiber frameworks in all the specimens.

CONCLUSION

Full-coverage design had significantly higher flexural and fracture strengths than box and tub-shaped designs. Since both values were noted to be in the order of masticatory stresses, the full coverage design is a good alternative for the replacement of missing molar teeth; however, the framework veneering composite interface was the weakest phase of FRC FPDs, thus indicating that further improvement in veneering composite or fiber framework is needed to improve the compatibility of veneering composite with that of fiber framework for long-term clinical implications.

Fracture Resistance of Composite Fixed Partial Dentures Reinforced with Pre-impregnated and Non-impregnated Fibers

BACKGROUND AND AIMS

The mechanical properties of fiber-reinforced composite fixed partial dentures (FPDs) are af-fected by fiber impregnation. The aim of this in vitro study was to compare the fracture resistance of composite fixed partialdentures reinforced with pre-impregnated and non-impregnated fibers.

MATERIALS AND METHODS

Groups (n=5) of three-unit fiber-reinforced composite FPDs (23 mm in length) from maxillary second premolar to maxillary second molar were fabricated on two abutments with pontic width of 12 mm. One group was fabricated as the control group with composite (Gradia) and the other two groups were fabricated with composite (Gradia) reinforced with pre-impregnated fiber (Fibrex ribbon) and non-impregnated fiber (Fiber braid), respectively. The specimens were stored in distilled water for one week at 37°C and then tested in a universal testing machine by means of a three-point bending test. Statistical analysis consisted of one-way ANOVA and a post hoc Scheffé's test for the test groups (α=0.05).

RESULTS

Fracture resistance (N) differed significantly between the control group and the other two groups (P<0.001), but there were no statistically significant differences between the pre-impregnated and non-impregnated groups (P=0.565). The degree of deflection measured (mm) did not differ significantly between the three groups (P=0.397), yet the mean deflection measured in pre-impregnated group was twice as that in the other two groups.

CONCLUSION

Reinforcement of composite with fiber might considerably increase the fracture resistance of FPDs; how-ever, the type of the fiber used resulted in no significant difference in fracture resistance of FPD specimens.

In vitro validation of a shape-optimized fiber-reinforced dental bridge

OBJECTIVE

To improve its mechanical performance, structural optimization had been used in a previous study to obtain an alternative design for a 3-unit inlay-retained fiber-reinforced composite (FRC) dental bridge. In that study, an optimized layout of the FRC substructure had been proposed to minimize stresses in the veneering composite and interfacial stresses between the composite and substructure. The current work aimed to validate in vitro the improved fracture resistance of the optimized design.

METHODS

All samples for the 3-unit inlay-retained FRC dental bridge were made with glass-fibers (FibreKor) as the substructure, surrounded by a veneering composite (GC Gradia). Two different FRC substructure designs were prepared: a conventional (n=20) and an optimized design (n=21). The conventional design was a straight beam linking one proximal box to the other, while the optimized design was a curved beam following the lower outline of the pontic. All samples were loaded to 400N on a universal test machine (MTS 810) with a loading speed of 0.2mm/min. During loading, the force and displacement were recorded. Meanwhile, a two-channel acoustic emission (AE) system was used to monitor the development of cracks during loading.

RESULTS

The load-displacement curves of the two groups displayed significant differences. For the conventional design, there were numerous drops in load corresponding to local damage of the sample. For the optimized design, the load curves were much smoother. Cracks were clearly visible on the surface of the conventional group only, and the directions of those cracks were perpendicular to those of the most tensile stresses. Results from the more sensitive AE measurement also showed that the optimized design had, on average, fewer cracking events: 38 versus 2969 in the conventional design.

SIGNIFICANCE

The much lower number of AE events and smoother load-displacement curves indicated that the optimized FRC bridge design had a higher fracture resistance. It is expected that the optimized design will significantly improve the clinical performance of FRC bridges.

Fracture resistance of three ceramic inlay-retained fixed partial denture designs. An in vitro comparative study

PURPOSE

The fracture resistance of ceramic inlay-retained fixed partial dentures (CIRFPDs) was studied.

MATERIALS AND METHODS

Thirty CIRFPDs were constructed using ice zircon milled ceramic material. Specimens were divided into three groups, 10 specimens each, according to the abutment preparation: inlay-shaped (occluso-proximal inlay + proximal box), tub-shaped (occluso-proximal inlay), and proximal box-shaped preparations. Each group was then subdivided into two subgroups of five specimens each, according to the span of the edentulous area representing a missing premolar or molar. All specimens were subjected to a fracture resistance test.

RESULTS

CIRFPDs with inlay-shaped retainers showed the highest fracture resistance values for missing premolars and molars. CIRFPDs with box-shaped retainers showed lower fracture resistance values. Statistical analysis revealed a significant difference between the three tested CIRFPD designs. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars and those constructed for the replacement of premolars. The CIRFPD constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All the fracture resistance values obtained in this study were superior to the assumed maximum mastication forces. Failure mode was delamination and chipping of the veneering material.

CONCLUSIONS

There was a statistically significant difference between the three designs of CIRPFDs tested. There was a statistically significant difference between CIRFPDs constructed for the replacement of molars than those constructed for the replacement of premolars. The CIRFPDs constructed for the replacement of molars gave lower fracture resistance values with the three tested designs. All fracture resistance values obtained in this study were superior to the assumed maximum mastication forces.

Immediate tooth replacement using fiber-reinforced composite and natural tooth pontic

The loss and replacement of anterior maxillary teeth poses several challenges. In patients refusing implant surgery, when minimal tooth reduction is desired, a fiber-reinforced composite fixed-partial denture may be used as a conservative alternative to a conventional fixed-partial denture for replacement of a single missing tooth. This article describes a clinical technique and six-year follow-up. The patient presented with a missing maxillary central incisor due to localized juvenile periodontitis. The abutment teeth were clinically stable. The advantage of supragingival margins and minimal tooth structure removal made the bonded bridge with a natural tooth pontic a viable procedure for this compromised restorative situation.

Fracture strength of bovine incisors after intra-radicular treatment with MTA in an experimental immature tooth model

AIM

To evaluate, using an experimental immature tooth model, the fracture resistance of bovine incisors submitted to different reinforcement treatments with mineral trioxide aggregate (MTA).

METHODOLOGY

An immature tooth model was created by sectioning the coronal and apical portions of 40 bovine incisors 8 mm above and 12 mm below the cementoenamel junction. The root canals were irrigated with 1.0% sodium hypochlorite. They were enlarged both coronally and apically using number 703 carbide burs (ISO: 500-104-168-007-021) and their internal diameter was standardized to 2.1 mm. The specimens were assigned to four groups (n = 10): GI-control (without filling); GII-apical MTA plug + filling with gutta-percha and endodontic sealer; GIII-filling with MTA; GIV-apical MTA plug + filling with MTA + metallic post (Reforpost I). A polyether impression material was used to simulate the periodontal ligament. The specimens were submitted to a compressive load at a crosshead speed of 0.5 mm min(-1) in a servo-hydraulic universal testing machine (MTS 810) applied at 45 degrees to the long axis of the tooth until failure. Data were submitted to statistical analysis by the Kruskal-Wallis test at 5% significance level.

RESULTS

GIV presented the highest fracture resistance (32.7N) and differed significantly from the other groups (P < 0.05). No statistically difference was found between GII (16.6N) and GIII (23.4N) (P > 0.05). GIII had a significantly higher fracture resistance than GI (P < 0.05).

CONCLUSIONS

The use of MTA + metallic post as an intra-radicular reinforcement treatment increased the resistance to fracture of weakened bovine teeth in an experimental immature tooth model.

Material characteristics of a novel shrinkage-free ZrSiO4 ceramic for the fabrication of posterior crowns

OBJECTIVE

To confirm the clinical applicability of a novel ZrSiO(4) (zircon) based shrinkage-free ceramic material, the flexural strength, fracture toughness and chemical solubility were tested. In addition, the fracture load of full crowns made from this material was tested after cyclic thermomechanical loading.

METHODS

Flexural strength of 12 specimens was measured using a biaxial bending test. Fracture toughness was measured using 10 slotted box shaped specimens. The specimens were fractured using a universal testing machine; fracture loads were recorded. A chemical solubility test was performed in accordance with ISO norm 6872. Additionally, 32 ZrSiO(4) all-ceramic crowns were fabricated on extracted caries-free human molars. Sixteen Empress 2 and 16 PFM crowns served as a reference control. After artificial aging of 1.2 million cycles in the chewing simulator, the survival rate of the crowns was determined. The fracture load of all surviving specimens was obtained by loading the crowns until fracture in a universal testing machine.

RESULTS

A flexural strength of 328MPa was found. The fracture toughness of the ZrSiO(4) ceramic was 5.16MPam(0.5). The chemical solubility amounted to 7.2microg/cm(2). All specimens survived the chewing simulation (survival rate: 100%); no crowns had to be re-cemented. A mean fracture strength of 1790N was found for Everest HPC for Empress 2 crowns, 1715N for Empress 2 crowns and 2416N for PFM crowns. Fracture loads of PFM crowns were significantly higher than for Empress 2 crowns (P=0.032) as well as ZrSiO(4)-crowns (P=0.007). There was no significant difference between ZrSiO(4)-crowns and Empress 2 crowns (P=0.743).

SIGNIFICANCE

At the present stage, Everest HPC can be recommended for the fabrication of single crowns as an alternative to conventional PFM and other all-ceramic crowns, because its fracture strength exceeds average masticatory forces in the posterior region.

Comparison of load-bearing capacity of direct resin-bonded fiber-reinforced composite FPDs with four framework designs

OBJECTIVES

This in vitro study was aimed to compare the fracture resistance of directly fabricated inlay-retained fiber-reinforced composite (FRC) fixed partial dentures (FPDs) with four types of framework designs.

METHODS

Forty-eight directly fabricated inlay retained FPDs were made of FRC and particulate resin composite (everStick/Tetric flow and Ceram). Extracted human mandibular first premolars and first molars were as abutments. The following framework designs were tested: in the Group A (control group), the framework was made of two prepregs of unidirectional glass FRC; the Group B, two prepregs in pontic portion were covered with one layer of multidirectional fiber veil FRC; the Group C, the FRC prepregs were covered in pontic portion with four short unidirectional FRC pieces along the main prepregs; in Group D, one short unidirectional FRC prepregs were placed on the main prepregs in 90 degrees angle to the main framework. After thermal cycling, FPDs of each group (n=12) were randomly divided into two subgroups (n=6). Fracture test was performed at the universal testing machine (1mm/min) where FPDs were loaded from the occlusal direction to the occlusal fossa or to the buccal cusp. Failure patterns were observed with stereomicroscope. Median and 25%/75% percentile values were calculated and nonparametric analysis was performed.

RESULTS

Compared with three other framework designs, the FPDs in Group D showed the highest resistance when loading to the occlusal fossa, with maximum load of 2,353.8N (25%/75%: 2,155.5/2,500.0) (p=0.000, 0.000, and 0.005 for compared with Group A, B, and C). The same group showed also higher resistance when loaded to the buccal cusp (1,416.3N (1,409.2/1,480.8)) if compared to the FPDs of the Group A and Group C (p=0.044, 0.010). In general the FPDs showed higher resistant to loading at the occlusal fossa (p<0.05).

CONCLUSIONS

This in vitro study showed that inlay-retained FRC FPD constructed with direct technique provided high fracture resistance. The framework design that provided support for the veneering composite of the pontic contributed to the highest load-bearing capacity even when loaded to the buccal cusp.

Influence of cavity preparation design on fracture resistance of posterior Leucite-reinforced ceramic restorations

STATEMENT OF PROBLEM

Controversy exists concerning the preferred cavity design for posterior ceramic restorations to improve their resistance to fracture under occlusal load.

PURPOSE

The aim of this study was to assess the resistance to fracture of leucite-reinforced ceramic restorations placed on molars with different cavity preparation designs.

MATERIAL AND METHODS

Ninety noncarious molars were selected, stored in 0.2% thymol solution, and divided into 9 groups (n = 10): IT, intact teeth; CsI, conservative inlay; ExI, extensive inlay; CsO/mb, conservative onlay with mesio-buccal cusp coverage; ExO/mb, entensive onlay with mesio-buccal cusp coverage; CsO/b, conservative onlay with buccal cusp coverage; ExO/b, entensive onlay with buccal cusp coverage; CsO/t, conservative onlay with total cusp coverage; ExO/t, extensive onlay with total cusp coverage. Teeth were restored with a Leucite-reinforced ceramic (Cergogold). The fracture resistance (N) was assessed under compressive load in a universal testing machine. The data were analyzed with 1-way and 2-way analyses of variance, followed by the Tukey HSD test (alpha = .05). Fracture modes were recorded, based on the degree of tooth structure and restoration damage.

RESULTS

One-way analysis showed that intact teeth had the highest fracture resistance values. Two-way analyses showed no significant differences for the isthmus extention factor, but showed a significant difference for the preparation design type of fracture (P = .03), and also for the interaction between both factors (P = .013). The fracture mode observed in all groups tended to involve only restorations.

CONCLUSION

Within the limitations of this study, it was observed that cuspal coverage does not increase fracture resistance of the posterior tooth-restoration complex restored with leucite-reinforced ceramics.

Effect of pontic height on the fracture strength of reinforced interim fixed partial dentures

OBJECTIVES

This in vitro study evaluated the fracture load of interim FPDs made with various materials and pontic heights. The hypothesis was that different materials and pontic heights result in different fracture resistance.

METHODS

Groups of interim FPDs were fabricated with prosthodontic resin materials on two abutments with two different pontic heights (4.3 and 5.8 mm) and a pontic width of 4 units (19 mm) (n = 3). The following materials were tested: (1) a thermoplastic polymer (Promysan Star), (2) Promysan Star with a veneering composite (Vita Zeta), (3) a non-impregnated polyethylene fiber reinforced resin (Ribbond) with a veneering composite (Sinfony), (4) an impregnated fiber reinforced composite system (Targis/Vectris), and (5) a conventional poly methyl methacrylate (PMMA) (Biodent K+B, control group). After 5000 thermocycles, the FPDs were temporarily fixed with a provisional cement on the corresponding abutments and tested for fracture strength. One-way and two-way ANOVA and Bonferroni-Dunn's multiple comparison tests were performed for the statistical analysis (alpha = 0.05).

RESULTS

The mean fracture strength ranged from 83.0 to 625.9 N for a pontic height of 4.3 mm and from 97.2 to 893.7 N for a pontic height of 5.8 mm. Vectris/Targis FPDs of both pontic heights exhibited significantly superior fracture resistance compared to the corresponding Promysan, Promysan/Vita Zeta, Ribbond/Sinfony and Biodent groups. Except Biodent FPDs, fracture resistance of FPDs with a pontic height of 4.3 mm showed no significant differences compared to a pontic height of 5.8 mm for each material.

SIGNIFICANCE

Material type of the FPDs has a significant influence on the fracture strength, whereas pontic height has no significant effect (except control group).

Fracture Resistance of Inlay-retained Fixed Partial Dentures Reinforced with Fiber-reinforced Composite

In this study, the effect on the fracture load of inlay-retained composite fixed partial dentures (FPDs) caused by reinforcing them with fiber-reinforced composite (FRC) in different positions was examined. Experimental FPDs were fabricated using Estenia/EG Fiber (Kuraray Medical). Pontic reinforcement was then performed in one of the following three ways: reinforced the central area in a single line or in double straight lines, or reinforced the bottom in a curved line. The finding was that, when the area ranging from the connector to the bottom of the pontic was reinforced with FRC in a curved line, the fracture load of the FPDs tended to become higher. In addition, the FPDs fractured mainly at the veneering composite of the connector area. Based on the results of this study, it was concluded that reinforcement using FRC is effective, and that the veneering composite in the connector area needs to have sufficient strength to prevent the fractures.

Fracture resistance of the veneering on inlay-retained zirconia ceramic fixed partial dentures

AIMS

The aim of this in vitro study was to evaluate the fracture load of zircon frames veneered with a polymer glass holding box inlay-retained fixed partial dentures (FPDs). The influence of the position of the frame and the span length was tested. Additionally, the fracture load values of zircon frames veneered with a press ceramic were evaluated.

MATERIAL AND METHODS

Box inlay cavities were prepared on mandibular molars and premolars. Forty-eight FPDs were manufactured using industrially prefabricated zircon frames veneered with the polymer glass Artglass. Sixteen FPDs received individually manufactured CAD/CAM zircon frames veneered with a press ceramic. All FPDs underwent thermal cycling and mechanical loading (ML). The load to fracture was measured and fracture sites were evaluated.

RESULTS

Four polymer veneered FPDs showed fractures in the veneering material after ML. The mean fracture resistance ranged from 531 N to 727 N. No significant influence of frame localization could be observed. Significantly greater fracture resistance values were found in the ceramic veneered FPDs (1276 N to 1413 N). There was no significant effect of span length in the polymer veneered group or in the all-ceramic group, with the exception of a significant peak in fracture load value for intermediate span lengths in the polymer group with a localized occlusal zircon frame.

CONCLUSIONS

Polymer veneered FPDs with Y-TZP frames showed acceptable fracture resistance values, but they cannot yet be unreservedly recommended for clinical use. Fracture values for CAD/CAM manufactured Y-TZP frames combined with a press ceramic deserve further clinical investigation.

In vitro fracture resistance of four-unit fiber-reinforced composite fixed partial dentures

OBJECTIVES

The aim of this in vitro study was to investigate the influence of glass fiber-reinforcement on the fracture resistance of four-unit composite fixed partial dentures (FPDs) in the posterior region.

METHODS

A total of 70 FPDs were fabricated of the composites Sinfony, Vita Zeta and Targis. With each material, 10 FPDs were made without glass fiber-reinforcement and 10 were reinforced with the new glass fiber system EverStick. In addition, 10 FPDs were fabricated of the material combination Targis/Vectris. After thermocycling, all FPDs were loaded until failure in a universal testing machine. The FPDs were then cut and cross-sectional areas were examined by scanning electron microscopy (SEM).

RESULTS

The load to fracture of the fiber-reinforced FPDs lay between 615 and 1191 N, which was significantly greater than the values found with unreinforced FPDs (between 178 and 307 N). The highest values were found with the combinations Targis/Vectris (1191 N) and Sinfony/EverStick (1137 N). SEM showed that the FPDs with EverStick reinforcement not only exhibited fracture lines in the fiber-composite interface, but also more often in the area of the fiber-reinforcement than was the case with the FPDs with Vectris reinforcement. The load to fracture was not significantly dependent on fiber quantity or course of fracture.

SIGNIFICANCE

It may be concluded that the fracture resistance of four-unit composite FPDs can be significantly raised by glass fiber frameworks (p<0.05). The reinforcement effect of EverStick depended significantly on the composite used (p<0.05).

Fracture resistance of fiber-reinforced composite restorations with different framework design

OBJECTIVES

Veneer fracture and bond deficiency between framework and veneer are typical failures of fiber-reinforced inlay fixed partial dentures (FPD). An eccentric load point on the pontic was used in this study to investigate the fracture resistance of FPDs with different framework designs. As null hypothesis, it was assumed that fracture resistance was not influenced by the fiber framework supporting the veneer.

METHODS

Four groups of Vectris/Adoro FPDs (4 x n=10 each) were manufactured. Beams (25 mm length) of Vectris Pontic (parallel aligned) with (a) rectangular (3 x 3) sectional view and (b) circular sectional view (theta 3 mm) were directly veneered using Adoro. (c) Circular beams like "b" were modified, i.e. those on the upper side were coated with two layers of the cross-sectioned fiber mat Vectris frame. (d) Vectris Pontic fibers were "anatomically" placed in the pontic area and wrapped using Vectris Frame. The frameworks were constructed in a vacuum/pressure process. All FPDs were mounted in a restrained-end apparatus and thermally cycled and mechanically loaded (TCML: 6000 x 5 degrees C/55 degrees C; 1.2 x 10(6) x 50 N, 1.66 Hz). After TCML, the FPDs were loaded to fracture.

RESULTS

All FPDs surpassed TCML, with no visible damage to the veneer or framework. Without transversal enlargement of the framework, additional cross-sectioned fiber mats alone did not improve resistance to fracture (a: 573+/-158 N (mean, standard deviation given); b: 737+/-66 N; c: 694+/-93 N; d: 902+/-149 N). Fracture lines occurred only in the veneer; the fiber frameworks were never affected.

CONCLUSIONS

Anatomical enlargement of the fiber framework at the pontic area (height, width) to support the veneer material improves the fracture resistance of fiber-reinforced FPDs.

Stress distribution in fiber-reinforced composite inlay fixed partial dentures

STATEMENT OF PROBLEM

Fiber-reinforced composite inlay fixed partial dentures (FRCIFPDs) may be a reliable prosthetic solution. Clinical procedures involved in their fabrication have been defined, but little is known about their mechanical behavior.

PURPOSE

This in vitro study used the finite element (FE) method to investigate 3-dimensional (3-D) stress and strain distribution produced in a 3-unit FRCIFPD.

MATERIAL AND METHODS

A 3-D FE model (227,768 3-D tetrahedral elements) of a 3-unit FRCIFPD cemented onto box-shaped prepared teeth was developed. Stress and strain distribution generated by a maximum load of 196 N applied vertically or laterally to the FRCIFPD centrally, on an area of 4 +/- 0.1 mm 2 , was analyzed. The specimen used to acquire the geometry of the model was also used for mechanical compressive tests, with vertical and lateral loads, to validate the numerical model.

RESULTS

The peak values of stress, calculated on the outer and inner surfaces of the FRCIFPD, were localized in the connector areas. When a vertical load was applied, stress on the prepared teeth was concentrated at the cervical margin of the abutment preparation.

CONCLUSION

Within the limitations of this in vitro study, the results suggest that within the FRCIFPD, stress concentrates at the connector areas, and that in the prepared teeth, peak stress is at the cervical margin of the box of the preparation.

Influence of root embedment material and periodontal ligament simulation on fracture resistance tests

The aim of this study was to evaluate the influence of the embedment material and periodontal ligament simulation on fracture resistance of bovine teeth. Eighty bovine incisor teeth were randomized into 8 groups (n = 10), embedded in acrylic or polystyrene resin using 4 types of periodontal ligament simulation: 1 - absence of the ligament; 2 - polyether impression material; 3 - polysulfide impression material; 4 - polyurethane elastomeric material. The specimens were stored at 37°C and 100% humidity for 24 hours. Specimens were submitted to tangential load on the palatal surface at 0.5 mm/minute crosshead speed until fracture. The fracture modes were analyzed as follows: 1 - coronal fracture; 2 - cemento-enamel junction fracture; 3 - partial root fracture; 4 - total root fracture. Statistical analyses by two-way ANOVA and Tukey's test were applied (p < 0.05). The results showed that root embedment method and periodontal ligament simulation have a significant effect on fracture resistance. Artificial periodontal ligament modified the fracture modes.

Inlay-fixed partial dentures adhesively retained and reinforced by glass fibers: clinical and scanning electron microscopy analysis after five years

Fifty-three posterior glass fibre-reinforced composite inlay-fixed partial dentures (IFPDs) in 36 patients were followed for 5 yr. For statistical analysis, one IFPD per patient was randomly selected. The survival rate and influence of discrete predictors (gender, location) and continuous variables (age, abutment surfaces) were determined. Clinical observations were recorded by using modified United States Public Health System (USPHS) criteria. Replicas of 17 randomly selected abutments were analysed by scanning electron microscopy (SEM) for marginal adaptation and the results were compared by using a repeated-measures analysis of variance (anova). The main reason for failure was veneering material delamination from the framework. The cumulative survival rate after 5 yr was 73% (95% confidence interval: 57-89%) for not delaminating and 96% (95% confidence interval: 88-100%) for not debonding. No significant influence of the tested predictors was found. Significant changes between baseline USPHS criteria and counterparts recorded at recall were fractures of the veneering material (chipping), wear, surface texture, and staining. Significant margin changes were only found between baseline and 1 yr. Thereafter, marginal adaptation remained stable. After 5 yr, 90% of the margins were termed as perfect. It was concluded that hard-tissue saving IFPDs with the current design maintained acceptable retention and marginal integrity. Future studies should aim at reducing delaminations by searching for improved framework designs and materials.

Fibre reinforced composite dental bridge. Part I: Experimental investigation

This experimental investigation aims at revealing the mechanical behaviour and failure pattern of direct fibre-reinforced resin-bonded dental bridge with various designs. To evaluate the overall effects of some newly developed dental materials, in the experiment, genuine composite dental bridge specimens are prepared and tested. The ultimate load, stiffness and mode at the failure of the bridges are measured and compared with the design variations. A good agreement between test and some clinical observations is demonstrated. It is verified that the weakest region appears across the pontic-abutment interface in the composite bridges. This study suggests that the composite bridges reinforced by fibres and supported by adjacent teeth could be of a higher structural strength and stiffness; therefore would provide better clinical performances.

In vitro fracture resistance of posterior metal-ceramic and all-ceramic inlay-retained resin-bonded fixed partial dentures

STATEMENT OF PROBLEM

Inlay-retained resin-bonded fixed partial dentures (RBFPDs) are conservative prosthetic restorations; however, their resistance to fracture is not clear.

PURPOSE

The purpose of this study was to compare fracture loads of posterior complete coverage metal-ceramic restorations with all-ceramic inlay-retained RBFPDs.

MATERIAL AND METHODS

Thirty-two posterior ceramic RBFPD restorations were divided into 4 groups (n=8): (1) Complete metal-ceramic fixed partial dentures (MC-FPDs) fabricated of Ni-Cr-based alloy (Wirolloy) and veneered with a ceramic (IPS d.SIGN) as the control group; (2) inlay-retained metal-ceramic (MC RBFPDs) with the same materials as the control; (3) inlay-retained lithium disilicate (LD) glass-ceramic (IPS Empress 2) RBFPDs; and (4) inlay-retained zirconia-based (Z) ceramic (Cercon) RBFPDs. Control specimens were prepared to receive conventional complete MC-FPDs designed to include a 1.3-mm-circumferential, 90-degree flat shoulder with rounded angles. Inlay-retained RBFPD specimens were prepared with 2-mm occlusal reduction but without bevels at the occlusal or gingival margins. Specimens were loaded and fracture loads (N) measured at fracture with a universal testing machine at a crosshead speed of 1.0 mm/min and 250 kgf load cell. Data were analyzed with 1-way ANOVA and Duncan test (alpha=.001).

RESULTS

Fracture loads (mean +/- SD) were greatest for control specimens (1318.43 +/- 211.00 N) and Z-RBFPD (1247.70 +/- 262.51 N) specimens as compared to MC-RBFPD or LD-RBFPD (P < .001). MC-RBFPD exhibited the next highest fracture loads (958.01 +/- 194.29 N), and LD-RBFPD exhibited the significantly lowest values (303.23 +/- 92.54 N) of the materials tested (P < .001).

CONCLUSION

Inlay-retained zirconia-based ceramic RBFPDs demonstrated the greatest fracture resistance among all inlay-retained restorations tested.

Effects of two preparation designs and pontic distance on bending and fracture strength of fiber-reinforced composite inlay fixed partial dentures

STATEMENT OF PROBLEM

Joint fractures observed in Targis/Vectris inlay adhesive fixed restorations may be related to the preparation design.

PURPOSE

This in vitro study investigated the effects of the proximal tooth preparation design and the pontic distance on the fracture strength and the amount of bending of fiber-reinforced inlay adhesive fixed partial dentures.

MATERIALS AND METHODS

Forty extracted premolars and 40 molars were embedded in a PMMA resin to represent a premolar and molar mesiodistal separation distance of 7 mm and 11 mm, respectively. Two preparation designs were used (proximal box and tub-shaped). The sample size was 10 for each group. Fiber-reinforced inlay adhesive fixed partial dentures were fabricated by use of the Targis/Vectris system and luted adhesively to the teeth with Variolink luting agent. A vertical force was loaded to the center of the fixed partial dentures at a crosshead speed of 1 mm/min. The initial bending (mm) prior to fracture was evaluated by measuring the distance the test rod moved from a 10 N preload to fracture. The differences in the mean fracture strength and the average amount of bending as a function of the preparation designs and pontic distances were compared by use of a 2-way analysis of variance (alpha=.05). The specimens were examined optically for the type of failure with a stereomicroscope. The fracture surface of the specimens was examined by scanning electron microscopy, and radiography was used to investigate the surface morphological features at the failure sites and to determine the fracture mode. A chi-square test was used to identify the differences in the debonding rates between the types of preparation designs and the pontic distance (alpha=.05).

RESULTS

The mean fracture strength and the standard deviation of the fiber-reinforced inlay retained adhesive fixed partial denture group was 1368+/-212 N for the 7-mm tub group, 885+/-109 N for the 11-mm tub group, 1779+/-317 N for the 7-mm box group, and 1336+/-281 N for the 11-mm box group. The fracture strength was significantly higher in the 7-mm pontic distance (P<.001) and for the box-shaped tooth preparation (P<.001). The amount of bending was significantly greater in the 7-mm pontic distance (P=.025) and the box-shaped tooth preparation (P=.002). Debonding was observed only in premolar teeth and tub-shaped design groups.

CONCLUSION

The box-shaped tooth preparation may be considered for restoration of a missing single posterior tooth with fiber-reinforced inlay adhesive fixed partial dentures.

Fixed partial dentures: all-ceramics, fibre-reinforced composites and experimental systems

The aim of this in vitro study was to compare the fracture strength of three-unit FPDs (fixed partial dentures) and three-unit inlay FPDs after a simulated 5-year oral wearing period. The restorations were made of a pressable all-ceramic (Empress 2) and two specially designed, experimentally fixed partial dentures combining ceramics with dental composite. Three-unit FPDs and inlay FPDs were manufactured and were adhesively luted onto human molars. After thermal cycling and mechanical loading in an artificial environment, the fracture strength was determined. Zircon-based milled ceramic (Lava) three-unit FPDs were used as a control. The zircon ceramic and the fibre-based ceramic three-unit FPDs showed median fracture values between 1000 and 1400 N. For composite veneered zircon FPDs a fracture strength of about 800 N and for all-ceramic Empress 2 of about 350 N could be determined. The results for the inlay FPDs were between 1300 N and 1400 N for FRC/ceramic, 1000 N for zircon/composite and 500 N for all-ceramic restorations. The all-ceramic showed higher fracture resistance applied as inlay FPDs. The described hybrid techniques combining ceramics and composites could represent an interesting procedure for further investigations and, eventually, clinical implication.

Shear in flexure of fiber composites with different end supports

The integrity of fiber-reinforced composite (FRC) prostheses is dependent, in part, on flexural rigidity. The object of this study was to determine if the flexure behavior of uniform FRC beams with restrained or simply supported ends and various length/depth (L/d) aspect ratios could be more accurately modeled by correcting for shear. Experimental results were compared with three analytical models. All models were accurate at high L/d ratios, but the shear-corrected model was accurate to the lowest, more clinically relevant, L/d values. In this range, more than 40% of the beam deflection was due to shear.

In vitro resistance of reinforced interim fixed partial dentures

STATEMENT OF PROBLEM

Comprehensive restorative dental treatment often necessitates the use of interim fixed partial dentures (FPDs) with high stiffness, especially in long-span restorations or areas of heavy occlusal stress.

PURPOSE

This in vitro study evaluated the fracture load of interim FPDs made with various materials and span lengths.

MATERIAL AND METHODS

Groups (n = 3) of interim FPDs were fabricated with prosthodontic resin materials on 2 abutments with 3 different pontic widths of 3 units (12 mm), 4 units (19 mm), and 5 units (30 mm). The following materials were tested: (1) a thermoplastic polymer (Promysan Star), (2) Promysan Star with a veneering composite (Vita Zeta), (3) a nonimpregnated polyethylene fiber reinforced resin (Ribbond) with a veneering composite (Sinfony), (4) an impregnated fiber reinforced composite system (Targis/Vectris), and (5) a conventional polymethyl methacrylate, Biodent K+B, (control group). After 5000 thermocycles in 2 water baths at 5 degrees and 55 degrees C, the FPDs were temporarily fixed with a provisional cement on the corresponding abutments and subjected to 3-point bending until fracture by a universal testing machine. Statistical analysis consisted of an analysis of variance (ANOVA, 1-way, 2-way) and Bonferroni-Dunn's multiple comparisons post hoc analysis for test groups (alpha = .05).

RESULTS

Fracture resistance (N) differed significantly for 3 (mean: 640 +/- 146 N), 4 (626 +/- 229 N), and 5 unit (658 +/- 98 N) Targis/Vectris FPDs compared with the corresponding Promysan (284 +/- 21 N to 125 +/- 73 N), Biodent K+B (247 +/- 91 N to 218 +/- 85 N), and Promysan/Vita Zeta (95 +/- 15 N to 82 +/- 6 N) groups (P < .05). Significant differences were obtained for the 4 and 5 unit Targis/Vectris FPDs compared with the Sinfony/Ribbond FPDs (281 +/- 25 N - 252 +/- 74 N) for the corresponding pontic spans.

CONCLUSION

Within the limitations of this in vitro study the impregnated fiber reinforcement may considerably enhanced the fracture resistance of interim FPDs of different span lengths.

Marginal accuracy and fracture strength of ceromer/fiber-reinforced composite crowns: effect of variations in preparation design

STATEMENT OF THE PROBLEM

Targis/Vectris restorations provide excellent esthetics and clinical success; however, the relationship of their marginal accuracy and fracture strength to the tooth preparation design requires further investigation.

PURPOSE

The aim of this study was to evaluate the effect of variations in tooth preparation design on the marginal accuracy before and after cementation and on the fracture strength of the ceromer/fiber reinforced composite crown.

MATERIAL AND METHODS

Three metal dies with varying total occlusal convergence angles (6 degrees, 10 degrees, 15 degrees) were prepared. A total of 30 (10 for each angle) Targis/Vectris crowns were fabricated. The restorations were evaluated at 48 points on the entire circumferential margin with a stereomicroscope measuring in micrometers for margin adaptation before and after cementation. The specimens then were compressively loaded to failure in a universal testing machine. Marginal adaptation was analyzed with Kruskal-Wallis test and post-hoc Dunnett test (alpha=0.05). The fracture strength was analyzed with analysis of variance and the Scheffe adjustment at the 95% significance level. Fracture surfaces of the crowns were examined with a scanning electron microscope to determine the mode of fracture.

RESULTS

The smallest marginal gap was recorded in angled crowns with a 6-degree convergence (47 microm mean). The marginal gap of most (95.6%) of the crowns was within a clinically acceptable level (established as </=100 microm). The mean marginal gap increased significantly after cementation, with the largest increase in the 6 degree group (76 microm mean). The 6-degree angled crowns had a significantly higher fracture strength (1,543 N) than the more convergent crowns (1,366 N) (P<.001). Mean fracture strength of all the crowns was 1,390 N. Scanning electron microscope observation showed that all crowns exhibited a 2-phase fracture pattern: a crack and chipping of the Targis layer followed by adhesive failure.

CONCLUSION

Within the limitations of this experimental design, decreasing the axial convergence angle of the ceromer/fiber-reinforced composite crowns diminished their marginal gap and increased their fracture strength.

Stress distribution of inlay-anchored adhesive fixed partial dentures: a finite element analysis of the influence of restorative materials and abutment preparation design

STATEMENT OF PROBLEM

Indirect composite or ceramic fixed partial dentures (FPDs) have become an alternative to conventional metal-ceramic adhesive fixed partial dentures (AFPDs). Little information about the adequate restorative material and tooth preparation design for inlay-anchored AFPDs is available to the clinician.

PURPOSE

The purposes of this simulation study were: (1) to use 2-dimensional finite element modeling to simulate stresses at the surface and interface of 3-unit posterior AFPDs made with 6 different restorative materials, and (2) to investigate the influence of 3 different abutment preparation configurations on the stress distribution within the tooth/restoration complex.

MATERIAL AND METHODS

A mesio-distal cross-section of a 3-unit AFPD was digitized and used to create 2-dimensional models of the periodontal membrane, supporting bone, different restorative materials (gold, alumina, zirconia, glass-ceramic, composite, and fiber-reinforced composite), and different abutment preparation configurations (interproximal slots vs. 2-surface [MO, DO] vs. 3-surface [MOD]). A simulated 50-N vertical occlusal load was applied to the standardized pontic element. The principal stress within the restorative materials, stresses at the tooth/restoration interface, and surface tangential stresses at the level of the pontic were calculated in MPa from the postprocessing files and compared to each other.

RESULTS

All materials and tooth preparation design exhibited a similar stress pattern, with a definite compressive area at the occlusal side of the pontic, a tensile zone at the gingival portion of the pontic, and tensile stress peaks in the abutment/pontic connection areas. Among isotropic materials, standard non-reinforced composites exhibited better stress transfer and reduced tensile stresses at the adhesive interface than ceramics and gold. Optimized placement of the glass fibers within the composite resulted in similar stress distribution when tested in 2-surface abutment preparation configuration. There was no detectable influence of preparation design on the behavior of the pontic area. Among all 3 preparation designs, only the DO design exhibited almost pure compression at the interface.

CONCLUSION

Within the limitations of this simulation experiment, the composite materials tested demonstrated a resilient component that favored stress transfer within the tooth/restoration complex. Their clinical use, however, may be contraindicated due to insufficient strength and fracture toughness. The addition of extremely tough fibers to composites represents the most promising combination. Clinical trials are required to ensure that veneering composite can survive under clinical conditions.

Scientifically based rationale and protocol for use of modern indirect resin inlays and onlays

The desire to place esthetically pleasing, conservative, functionally stable, posterior restorative materials has steadily increased over the past 20 years. The creation of successful dentin bonding adhesives and appropriate resin luting cements has paved the way for the development of a myriad of indirect resin-based restorative materials. These materials have been specifically designed to overcome the negative attributes of their porcelain counterparts, and to simplify fabrication, insertion, and post-delivery adjustments. Possibly like no other product before, these restorative materials have met with instant clinical acceptance by many practitioners, and concern exists that these materials have not been sufficiently studied to warrant such widespread acceptance. This article presents an overview of the history and development of resin-based, esthetic, indirect systems, and offers the clinician a review of the literature supporting their role in posterior restorative dentistry. Additionally, a scientifically based protocol for preparation, impressing, provisionalization, and subsequent cementation and adjustment of indirect laboratory-processed resin inlays and onlays is presented.

Flexural properties of fiber reinforced composite using a vacuum/pressure or a manual adaptation manufacturing process

PURPOSE

This study investigated the influence of fiber content and water storage on the flexural strength of beams made of two fiber-reinforced composites (FRC), the Vectris and the FibreKor system.

MATERIAL AND METHODS

A manual adaptation method (FibreKor, n=30) and a vacuum/pressure process (Vectris, n=30) were compared using 25x4x2mm(3) beams. One group of the Vectris (n=10) and the FibreKor beams (n=10) was stored in water for 24h, a further group was thermal-cycled (TC) 6000x5 degrees C/55 degrees C, and a third group was stored in water for 30days at 37 degrees C. All beams were then loaded to failure using a three-point bending test and the flexural strength was calculated. Finally, the fiber volume percent (vol%) was determined.

RESULTS

Generally, the flexural strength decreased significantly with increasing storage time independent of the investigated fiber- and/or manufacturing system. With the parameters 24h/TC/30days, the mean of flexural strength for the Vectris beams was 618/579/545N/mm(2), and for FibreKor 585/534/499N/mm(2). A fiber content of 28.1+/-0.4vol% was assessed for the Vectris beams and 12.8+/-0.6vol% for the FibreKor beams. After 24h storage in water, the Vectris and the FibreKor beams demonstrated a statistically significant higher flexural strength than after 30days storage in water.

CONCLUSIONS

A vacuum/pressure manufacturing process in contrast to manual adaptation, resulted in a markedly higher fiber content, but did not necessarily lead to significantly higher flexural strength. Not only the fiber content, but also matrix composition as well as the bond between fibers and matrix determined the properties of FRC.

Clinical and scanning electron microscopic evaluation of fiber-reinforced inlay fixed partial dentures: preliminary results after one year

STATEMENT OF PROBLEM

Restorative dentistry searches for nonmetal reinforcement of esthetic fixed partial dentures (FPDs).

PURPOSE

This clinical study evaluated conservative fiber-reinforced composite FPDs bonded to inlay abutments.

MATERIAL AND METHODS

Twenty fiber-reinforced composite inlay FPDs were made for 15 patients. Restorations were manufactured with the Targis Vectris glass-fiber-reinforced composite system and a simplified laboratory technique. The 20 bonded inlay FPDs were examined clinically and by SEM after 1 year.

RESULTS

All 20 FPDs were intact at the 1-year examination. There were no signs of fracture, surface defects, or excessive wear with SEM. SEM marginal analysis exhibited 91.6% +/- 5% excellent margins at the tooth-luting composite interface and 86. 1% +/- 8% excellent margins at luting composite/restoration interface.

CONCLUSION

On the basis of the results of this descriptive study, bonded glass-fiber-reinforced composite inlay FPDs were considered clinically successful at the 1-year examination.